The present invention relates to a voltage converter. More specifically, the invention relates to improvement of a charge pump type voltage converter.
Voltage converters include chopper type switching system, fly-back converter, forward converter, charge pump type converter and the like, and they are used properly according to applications. FIG. 13 shows a charge pump type 1-step-up converter. As shown in the drawing, two sets of relay switches S13 and S14 and relay switches S15 and S16 which interlock, two capacitors C11 and C12 are provided between a power supply 3 and an output terminal. C11 is a pump capacitor, and C12 is a reservoir capacitor. The two sets of relay switches are turned on/off alternatively so that the pump capacitor C11 and the reservoir capacitor C12 are charged alternatively and performs a step-up operation.
For example, when the power supply 3 is set to DC 12 V, a load 4 is set to 100xcexa9, SSR (solid state relay) or MOS relay is used as a relay and an operation speed is 0.1 ms, an output voltage characteristic is as shown in FIG. 14. Here, in FIG. 14, the pump capacitor is set to 100 xcexcF. and reservoir capacitor is set to 100 xcexcF.
When the voltage converters are compared with each other, a chopper switching type voltage converter requires a coil, and a fly-back converter or a forward converter requires a transformer. For this reason, these converters are not convenient for the case where they are miniaturized, and become expensive. Moreover, their circuit configuration is complicated, and an adjustment operation is troublesome.
In addition, as for a charge pump type voltage converter, as shown in FIG. 13, coil and transformer are not required so that its circuit can be configured at low price, but it is difficult for this converter to cope with high load (high output current). As shown in FIG. 14, in the case where a 12 V power supply is raised by 1 step so that a load of about 4 W is driven, the output voltage cannot obtain a satisfactory step-up value so as to become unstable. As a result, the output voltage cannot cope with the load.
This is because a switching speed and on-resistance of SSR or MOS relay do not obtain satisfactory values. Even if the SSR or MOS relay is changed into a MOS analog switch, for example, high-speed switching is possible but the on-resistance is large. As a result, the above problem cannot be solved. Moreover, on-resistance of a mechanical relay is small but high-speed switching is impossible so that the problem cannot be solved.
In order to solve the above problem, the inventors pay attention to that if on-resistance is small and high-speed operation can be performed in a relay to be used for a charge pump type voltage converter, the above problem is solved and a voltage converter of small size, high output, high voltage and high efficiency can be realized at low price. Therefore, an object of the present invention is to provide a voltage converter which has small size, high output, high voltage and high efficiency although this voltage converter is of a charge pump type.
In order to solve the above problem, a first aspect of the invention provides a charge pump type voltage converter having a pump capacitor, a reservoir capacitor and a plurality of switch elements, characterized in that the switch elements are composed of piezo-electric relays, and actuator sections of the piezo-electric relay have a shape holding layer, an operating section having at least a pair of electrodes formed on the shape holding layer, a vibration section for supporting the operating section and a fixing section for supporting the vibration section vibratingly, and the vibration section and the fixing section are formed integrally by ceramic, and the shape holding layer is composed of a piezo-electric and/or electrostrictive layer and/or an anti-ferroelectric layer.
A second aspect of the invention provides the voltage converter depending from the first aspect, characterized in that the switch elements and the pump capacitor and/or the reservoir capacitor are formed integrally on one substrate.
A third aspect of the invention provides the voltage converter depending from the first or second aspect, characterized in that contact points of the piezo-electric relays are composed of a movable terminal which moves up and down due to deformation of the operating section and a counter terminal plate which faces an upper surface of the movable terminal.
A fourth aspect of the invention provides the voltage converter depending from the first, second or third aspect, characterized in that one switch element is composed of a plurality of piezo-electric relays, and when the piezo-electric relays perform on/off operations simultaneously, the switch elements are opened and closed.
A fifth aspect of the invention provides the voltage converter depending from the first through fourth aspects, characterized by including the piezo-electric relays which can be driven by an input voltage,
A sixth aspect of the invention provides the voltage converter depending from the fifth aspect, characterized in that a groove is provided on the substrate between adjacent operating actions.
A seventh aspect of the invention provides the voltage converter depending from the fifth or sixth aspect, characterized in that the voltage converter is of a step-up type that a DC voltage on the output aside is larger than an input voltage.
An eight aspect of the invention provides the voltage converter depending from the first through seventh aspects, characterized by including a sub-power supply section having the piezo-electric relays which can be driven by the input voltage and a main power supply section having the piezo-electric relays which can be driven by the output voltage.
A ninth aspect of the invention provides the voltage converter depending from the eighth aspect, characterized in that the sub-power supply section is first operated so as to generate a raised output voltage, and the main power supply section starts to operate.
A tenth aspect of the invention provides the voltage converter depending from the ninth aspect, characterized in that detection means for detecting the start of operation of the main power supply section is provided to the sub-power supply section, and the sub-power supply section is provided with stopping means for receiving a detection signal from the detection means so as to stop the driving
An eleventh aspect of the invention provides the voltage converter depending from the tenth aspect, characterized in that the stopping means is composed of the piezo-electric relay which is driven by the raised output voltage of the main power supply section.